Cisco 3750 Stacking Configuration

Process for replacing a failed master switch in a Cisco 3750 switch stack

1. Upgrade or downgrade the software on the replacement switch to match the rest of the switch stack

The version of IOS running on the switch must match the other switches in the stack exactly. IOS images used on CHPC switches can be found on the TFTP server, megatron.chpc.utah.edu in /tftpboot/images/cisco . To see what version is running on one of the functional switches, use show version:

System image file is “flash:c3750-ipbasek9-mz.122-44.SE/c3750-ipbasek9-mz.122-44.SE.bin”

….. (output omitted) ….

The line “System image file is …” will show the image name that needs to be used. Find this image name (with a “-tar” in it) either on megatron or on the Cisco web site.

Once you have identified which version of IOS to use, connect the switch to the network using an IP address that is available (such as a moria address). To do this, bring up a VLAN interface on VLAN1 and connect the switch to the network. VLAN1 is used because all of the ports on the replacement switch will already be in that VLAN, and all you have to do is find a port on the network and plug in. Also, turn off spanning tree to speed up bringing up the link.

You’ll be asked to confirm the change, and then get a message about reloading the switch.

Reload the switch and continue with step 3 below.

3. Change the switch priority

The master switch in a stack is the one with the highest priority. To make sure that this new switch becomes the master, make its priority the same or higher than the failed switch. If you don’t remember what the failed switch’s priority is, just run show switch on one of the remaining functional switches and make sure that the priority that you assign to the replacement master switch is higher than the priority for the slave switches. Set the priority like this:

(config)#switch 1 priority <priority>

4. Power down the entire stack and disconnect the failed master switch

The entire stack will lose its configuration when the master switch is replaced. This is okay, because we regularly back up our configs, right? Make sure to note the pattern of how the cables plug in so that you can plug them in to the new switch in the same way.

5. Connect the new master switch and power up the stack

Connect everything up. Make sure to use a screwdriver to tighten up the stacking cables, as they have pretty shallow receptacles.

6. Configure the uplink ports and assign an IP address to the master switch

In order to restore the backed-up configuration, you’ll have to get some kind of network access working on the switch. Usually, this will mean configuring a portchannel and setting up some VLANS. Check the configuration on the remaining functional switches in the stack to see what VLANs to use, etc.

7. Pull down the backed-up configuration from the TFTP server

delicate_stack2# copy tftp run

and follow the prompts for TFTP server and file name. Once the configuration is finished copying, everything should be up.

8. Verify stacking

Verify that the stack is configured as expected. Use show switch and make sure that switch 1 is the master:

1. Upgrade or downgrade the software on the replacement switch to match the rest of the switch stack

The version of IOS running on the switch must match the other switches in the stack exactly. IOS images used on CHPC switches can be found on the TFTP server, megatron.chpc.utah.edu in /tftpboot/images/cisco . To see what version is running on one of the functional switches, use show version:

System image file is “flash:c3750-ipbasek9-mz.122-44.SE/c3750-ipbasek9-mz.122-44.SE.bin”

….. (output omitted) ….

The line “System image file is …” will show the image name that needs to be used. Find this image name (with a “-tar” in it) either on megatron or on the Cisco web site.

Once you have identified which version of IOS to use, connect the switch to the network using an IP address that is available (such as a moria address). To do this, bring up a VLAN interface on VLAN1 and connect the switch to the network. VLAN1 is used because all of the ports on the replacement switch will already be in that VLAN, and all you have to do is find a port on the network and plug in. Also, turn off spanning tree to speed up bringing up the link.

2. Change the switch number to match whatever the failed switch number was

First, figure out what the replacement switch’s current number is:

delicate_stack2#sh switch

Switch/Stack Mac Address : 0017.5a33.f180

H/W Current

Switch# Role Mac Address Priority Version State

———————————————————-

*2 Member 0016.9dba.9800 14 0 Ready

This switch’s number is 2

(config)# switch2 renumber <switch number from the failed switch>

You’ll be asked to confirm the change, and then get a message about reloading the switch.

Reload the switch and continue with step 3 below.

3. Change the switch priority

The master switch in a stack is the one with the highest priority. To make sure that this new switch does not become the master, make its priority lower than the master switch. You can run show switch on the master switch to see what the current priorities of the other switches in the stack are. Set the priority like this:

(config)#switch1 priority <priority>

4. Power down the failed switch and disconnect it from the stack

The other switches in the stack can stay up and passing traffic while you remove this switch. Make sure that you note the position of the stacking cables.

5. Connect the new switch and power it up

Connect everything up. Make sure to use a screwdriver to tighten up the stacking cables, as they have pretty shallow receptacles.

6. Verify stacking

Verify that the stack is configured as expected. Use show switch and make sure that switch 1 is the master:

delicate_stack2#show switch

Switch/Stack Mac Address : 0017.5a33.f180

H/W Current

Switch# Role Mac Address Priority Version State

———————————————————-

*1 Master 0017.5a33.f180150 Ready

2 Member 0016.9dba.9800140 Ready

3 Member 0024.5038.e200 13 0 Ready

Make sure to save the configuration before you leave:

delicate_stack2# wr

Building configuration…

[OK]

Other Notes

Find the serial number on a switch

Using show inventory you can get the serial number info from all of the switches in the stack:

delicate_stack2#show inventory

NAME: “1″, DESCR: “WS-C3750G-24T”

PID: WS-C3750G-24T-S , VID: V07, SN: CAT1010Z1LX

NAME: “2“, DESCR: “WS-C3750G-24T”

PID: WS-C3750G-24T-S , VID: V06, SN: CAT0951N3DS

NAME: “3“, DESCR: “WS-C3750G-24T”

PID: WS-C3750G-24T-S , VID: V07, SN: FDO1248X3LN

Back up the configuration to the CHPC TFTP server

When you are finished replacing everything, make a backup to the CHPC TFTP server at megatron.chpc.utah.edu. Create a directory on megatron in /tftpboot/configs with the current date, in the format of YYYY-MM-DD. Usecopy run tftp to get it done:

delicate_stack2#copy run tftp://155.101.3.109/configs/2010-06-25/delicate-stack2

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